Stocks slipped Friday as volume rolled in mixed despite an options expiration day. The Nasdaq and NYSE composite lost 0.2% each, while the S&P 500 shaved off 0.1%. The IBD 50 dropped 0.4%. Volume rose on the NYSE but fell on the Nasdaq. Friday was an options expiration day, which usually boosts volume. Wal-Mart Stores (WMT) sent a shiver through the market. The stock slashed 2% lower in triple volume. A Bloomberg story said Wal-Mart was seeing the